Antibiotics Are Unlikely Major Contributors to Childhood Obesity

Antibiotics do not appear to be associated with childhood obesity.

Antibiotics do not appear to be associated with childhood obesity, according to study results published in JAMA Network Open.

Antibiotics have been used as growth-promoting agents in farm animals and have subsequently been associated with obesity in mice. However, the evidence of this association in humans is conflicting. Previous studies that demonstrated a positive association between antibiotics and obesity did not adequately account for potential cofounders, including environmental and genetic factors, and have not examined siblings or twins to account for possible unmeasured confounders. Previous studies that showed a negative association, which included siblings and twins, found no association between antibiotic exposure and risk for childhood obesity.

However, these studies consisted of small cohorts and did not include national data or analyses on both siblings via singleton pregnancies or via multiple gestation pregnancies (twins). Therefore, using national data, this cross-sectional study, conducted in New Zealand, assessed whether antibiotic exposure during pregnancy and/or early childhood is associated with the development of childhood obesity while focusing on siblings and twins.

A total of 284,211 participants were included in the study: 151,359 children and 132,852 mothers. The main outcome was odds of obesity in children at age 4 years. Using covariate adjusted analyses, data was analyzed from 150,699 children who had available data (30,696 siblings and 4188 twins). Using fixed-effects analyses, data was analyzed from 6249 siblings and 522 twins with discordant outcomes. Data was collected from a national health screening program that records height and weight of children aged 4 years in New Zealand and these data were linked to pharmaceutical records for the evaluation of antibiotics dispensed to women before conception during all 3 trimesters of pregnancy and to their children from birth to 2 years of age.

In total, >1 course of antibiotics was dispensed to 35.7% of mothers and 82.3% of children during the first 2 years of life. Results of the covariate adjusted analyses showed that both prenatal and childhood exposure to antibiotics were independently associated with pediatric obesity at age 4 years in a dose-dependent manner. Every additional course of antibiotics dispensed to the mothers yielded an adjusted odds ratio (aOR) of obesity in their children (siblings) of 1.02; this is largely the same magnitude of association seen in the whole population.

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With regard to the child’s exposure, the aOR was 1.04 among siblings and 1.05 among twins for the association between antibiotic exposure and obesity. However, no association between antibiotic exposure and obesity was seen in the fixed-analyses of siblings and twins. The aORs were 0.95, 1.02, and 0.91 for maternal exposure, child’s exposure, and twins’ exposure, respectively. These discordant results likely reflect unmeasured confounding factors (host genetics, infection, maternal body mass index, etc) and may be explained by sharing of the untreated sibling’s microbiome.

Overall, the study authors concluded that, “Although judicious use of antibiotics is necessary, antibiotics are unlikely to be a major contributor to childhood obesity.”


Leong KS, McLay J, Derraik JG, et al. Associations of prenatal childhood antibiotic exposure with obesity at age 4 years. JAMA Network Open. 2020;3(1):e1919681.